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Chucks.—Four examples of Whiton's chucks are shewn in
Pigs, 150, 151, 152, and 153. The Independent Chuck (Fig, 150)
Is really a dog chuck. The screws may be turned by a square
key at A, so far as to release the jaws altogether, which, being
reversed, as at n, serve to hold drills when boring stationary work,
or to take a longer grip on rotating work. Pig. 151 is a good
example of a concentric or l universal* scroll chuck. Applying a
key to the bevel pinion c, the wheel D is rotated, carrying on its
opposite surface what, on reference to front view, is seen to be a



spiral having three or four turns in its whole travel. The rotation
of this * scroll' moves the jaws nearer to or farther from the centre,
but equally, thus centreing and gripping the work at the same
time. Fig. 152 is a Lever Chuck having a scroll, but no gearing.
A tommy is inserted at E to turn the scroll F, while the rest of the
chuck GO is stationary, All these chucks are fastened to the
mandrel in the same manner, by bolting to a small face plate
screwed on the mandrel,

9 The Drill Chuck (Fig. 153) has the back portion H screwed on
tlie mandrel, vrhile the front part j carrying the jaws may be rotated;
the scrall is therefore stationary while the jaws are carried round
it Hand tightening is sufficient for small drills, the surface of j
being roughened for grip; greater tightness is obtained by using